Interesting
Do you just let them build up on spring flow and add supers for summer flow if not on early crops such as osr ..whats your method of swarm control while dealing with 3 brood boxes ?
Plenty of brood space early is the key, but brood congestion from spring nectar
must be avoided so supers must go on at the same time.
From the bottom box a few frames of open brood are raised into the centre of the new box, which draws bees up and deters them from using the new upper brood as a super (they will, if a spring flow is strong).
Bottom box is re-filled with drawn comb (if I have it), alternated with full combs. Super is added, probably two, depending on area and flow and forecast (assesstimate).
Not long after and before peak laying, the third brood box is put between the first two; open brood combs are added as before, acting as a bridge. Maybe another super is given. Unfinished foundation is added alternately into the middle of the nests, expanding the colony laterally as well as vertically.
Such rapid addition of space gives bees work but though it reduces swarming, the inevitable cannot be eliminated. I check two or three centre combs in the top box, take it off, then do the same in the middle box. Usually ignore the bottom box unless polished or loaded cups have been found above.
If on your next visit you find untouched brood foundation, expect swarming. If time is short, a quick look lift & look under the top two broods may reveal loaded cups or QCs; I wouldn't rely on that but may get away with it.
If QCs are found I do a vertical split, often three or four in the same stack if the colony is good. The bottom box is standard AS - queen, foundation, flyers. The stronger splits get the supers, and the upper a QX a month later when the queen starts laying (by then I'll have found a few QXs at the back of a shed).
Once the queens are mated and laying I take out a 3 or 4-frame nuc and unite the stack to the bottom entrance. If nucs are needed strong they go off-site, but as the main flow is not far off, nucs in the same apiary allows the foragers to return to work for the main colony. Bees soon work out the reduction to one entrance. The small nucs have plenty of time to build before wasps & winter appear.
At this point the colony will have three broods and two or three supers; one or two more supers go on, the main flow opens and the slog is over.
When the top brood is full of honey the QX can be taken out, because queens are unlikely to cross that expanse of honey and the absence of a QX allows house bees to unload more rapidly. Alternatively, the QX can be put on top of the second brood, where it stays in case a block of fondant is needed at the end of the year.
Bees work far faster than humans and for many years I lagged behind in giving space early enough and in sufficient quantity, so ran around struggling with sweaty swarming.
The trick is to recognise the speed at which colonies build and to be flexible and ready to take advantage of it; this surprises newer beekeepers, perhaps influenced (as I was) by the rigid catalogue set-up of one brood and two supers.